In general, a conventional semiconductor light-receiving device has a pin junction epi-wafer that includes an n-type buffer layer, an I-type light absorbing layer and a p-type cap layer laminated on a semiconductor substrate. In a semiconductor light-receiving device, disclosed in Japanese Laid open patent publication H7-202263, a light-receiving section is formed on a semiconductor substrate by shaping layered structure into a preferable shape.
One side-(wall) surface of the light-receiving section is a light-receiving surface, which is arranged vertical to the upper surface of the semiconductor substrate. An electrode is formed on the p-type cap layer of the light-receiving section; and an electrode is also formed on the back surface of the substrate.
In the semiconductor light-receiving device, light is not wave-guided to the I-type light absorbing layer inside the device. Therefore, the coupling efficiency of light cannot be improved and the density of the electric charge becomes high only around the light-receiving surface. As a result, a deterioration of the signal frequencies is extracted through the buffer layer or the cap layer. Providing a wave-guiding channel structure having a wave-guiding channel may solve this problem. The wave-guide channel structure wave-guides light to the I-type light absorbing layer inside the device; however, the application of the wave-guiding channel structure significantly increases the manufacturing cost of semiconductor light-receiving devices and is thus impractical.
The light-receiving surface may be curved to improve the coupling efficiency of this semiconductor light-receiving device, thus enlarging the exposed area of the I-type light absorbing layer relative to the light-receiving surface. Even though, however, an improvement in the coupling efficiencies is attempted by increasing the exposed area of the I-type light absorbing layer relative to the light-receiving surface with e.g., the curved light-receiving surface, the coupling efficiency is still small and there is still technical dissatisfaction over a deterioration of frequencies.